Thanks for all the help so far.
I used a refractive index calculator (Snell's Law Calculator, Refractive Index Calculator -- EndMemo) to calculate the angle of light rays passing through glass & air to design this lens.
Edit: Oh no… I accidentally reversed the IOR’s of the air and glass, so my diagram is totally wrong.
I managed to magnify the background with this lens.
I’m hopefully going to add another lens to increase the magnification.
The distortion is terrible though… Hopefully going high poly isn’t the only fix because last time my lenses had over 100,000 edges. 
Any help with the distortion would be greatly appreciated. Even at 100,000+ edges, there’s still distortion.
Edit: Changed IOR from 1.520 (crown optical glass) to 1.6 (flint glass)
P.S. Most telescopes try to focus the light, but I think dispersing the light will help you see smaller rays of light by getting the peripheral information out of the way. I think the goal should be to gather the smallest rays of light possible, then enlarge them into an image.
Edit:
Interesting… I found out that geodesic spheres and revolved spheres have different types of distortion.
Meshes:
Revolved Sphere
Geodesic Sphere:
The distortion is terrible…